Background colour of docked windows

[Unit2Ed]

Version/Branch of Dear ImGui:

Version: 1.72 WIP (17102) Branch: docking

Back-end/Renderer/Compiler/OS

Back-ends: imgui_impl_dx11.cpp + imgui_impl_win32.cpp Compiler: Visual C++ 2017 Operating System: Windows 10

Docked windows currently have the flag ImGuiWindowFlags_ChildWindow added to them automatically, which causes them to use ImGuiCol_ChildBg rather than their normal ImGuiCol_WindowBg. Do you think it would be reasonable to add an exception to GetWindowBgColorIdxFromFlags so that they continue to use ImGuiCol_WindowBg if the window's docked?

We have some windows with background colours that differ from the style's default, and this change makes them inconsistent. To workaround it we would need to also adjust ImGuiCol_ChildBg on every dockable window, and pop it immediately after Begin so that any "real" child windows within them are drawn with the proper ImGuiCol_ChildBg.

ImGuiWindowFlags window_flags = ImGuiWindowFlags_MenuBar | ImGuiWindowFlags_NoDocking;

ImGuiViewport* viewport = ImGui::GetMainViewport();
ImGui::SetNextWindowPos(viewport->Pos);
ImGui::SetNextWindowSize(viewport->Size);
ImGui::SetNextWindowViewport(viewport->ID);
ImGui::PushStyleVar(ImGuiStyleVar_WindowRounding, 0.0f);
ImGui::PushStyleVar(ImGuiStyleVar_WindowBorderSize, 0.0f);
window_flags |= ImGuiWindowFlags_NoTitleBar | ImGuiWindowFlags_NoCollapse | ImGuiWindowFlags_NoResize | ImGuiWindowFlags_NoMove;
window_flags |= ImGuiWindowFlags_NoBringToFrontOnFocus | ImGuiWindowFlags_NoNavFocus;

ImGuiDockNodeFlags dockspaceFlags = ImGuiDockNodeFlags_PassthruCentralNode;
if (dockspaceFlags & ImGuiDockNodeFlags_PassthruCentralNode)
    window_flags |= ImGuiWindowFlags_NoBackground;

ImGui::SetNextWindowSize(ImVec2(640, 480), ImGuiCond_Always);
ImGui::Begin("Dock", nullptr, window_flags);
ImGui::PopStyleVar(2);
ImGuiID dockspaceID = ImGui::GetID("DockSpace");
ImGui::DockSpace(dockspaceID, ImVec2(0, 0), dockspaceFlags);
ImGui::End();

ImGui::PushStyleColor(ImGuiCol_WindowBg, ImVec4(1.0f, 0.0f, 0.0f, 1.0f)); // Set window background to red
ImGui::Begin("Red Window");
ImGui::PopStyleColor();
ImGui::End();

[ocornut]

Hello,

The reasoning behind this choice is that the root/host docking window handle displaying the entire background. Individual docked windows because ChildBg default to zero wouldn't display anything again, to save on fillrate and avoid situation where where alpha <1.0 we would end up with a different final color (because two layers would blend).

You are however right it should be using WindowBg. An easy but slightly incorrect workaround:

• Always use WindowBg but only display it for each individual docked window if the value of WindowBg differs from the one of the parent/host window.
• That would still fail to render the correct final color if alpha < 1.0f, and would generally be a little fishy/obtuse, but may be good enough.

One correct but tricky solution would be:

• That the parent/host window would only display its background in the small gaps between windows and behind tab bars, and individual docked window are in charge of displaying their section of the background.
• But there's another edge case: if the docked window stop being submitted, the corresponding dock node would have no background for 1 frame. So at the end of the frame we would need to detect this case and have the parent/host wnidow fill in the missing part.
• This idea would potentially be simplifed by having the parent/host window submit all the vertices ahead, and have whichever docked window are submitted and visible update the color of those vertices.

On your side, in the short term you may also consider just drawing a background color of your choice yourself.

[ocornut]

(Addenum: commit 9e4956d86bf6cbb8a10df210cba2e70857cd3eb0 referring incorrectly to #2700 where it actually wanted to refer to #3521.)

[ocornut]

FYI I've been working on that yesterday: (#2700, #2539)

I've got a "mostly working" version but there are many edge cases that are currently tricky to solve and would lead to "holes" in the background for 1-2 frames. At the moment I believe the fully correct version would require too much work (maybe a few days) as it would requires reoverhauling some aspect of how docking nodes gets updated mid-frame. I however think it will be healthy for the code to do that reoverhaul, and for many more reasons that just override WindowBg color, so I'll eventually do it. But for now I left this stashed.

(Note that I pushed another commit yesterday which makes the Docking system honor changes of ImGuiCol_Tab*** colors and text colors, so it is possible to make specific windows have a colored tab.)

[ocornut]

This is now properly solved by b16f738

It turned out a bit difficult but still easier than I thought. One key element was fixing two other bugs a bit earlier (8733ca4).

I needed to rework this because we have another task (newly appearing windows showing behind modals) which required a rework of our dimming layers, which required a rework of how background layers were rendered, so this come in the yak-saving pile.

Also fixed #2539 and #2522 all-together.

[ocornut]

Temporarily reverting this at it is causing a problem with dimming overlay (ctrl+tab, modals) in dock trees.

[ocornut]

Amend/fix with b40c54d

[loryruta]

Version/Branch of Dear ImGui:

Version: 1.87 Branch: docking Commit: 1ee252772ae9c0a971d06257bb5c89f628fa696a

Back-end/Renderer/Compiler/OS

Back-ends: imgui_impl_vulkan.cpp + imgui_impl_glfw.cpp Compiler: Visual Studio 2019 Operating System: Windows 10

---

Hi, I'm writing my problem here because it seems to be related:

I have a main window hosting a DockSpace with ImGuiWindowFlags_NoBackground and a window with a semi-trasparent background (alpha = 0.1). If I dock the latter within the no-background window its background doesn't get blended correctly: it's still transparent but not the same as when it wasn't docked (I guess because it gets blended with some black color (?)).

Here's what is happening:

https://user-images.githubusercontent.com/24776968/159745725-92a287b3-88b5-4da1-bb87-206f849dc996.mp4

And here's the code I'm using:

ImGuiViewport* viewport = ImGui::GetMainViewport();
ImGui::SetNextWindowPos(viewport->Pos);
ImGui::SetNextWindowSize(viewport->Size);
ImGui::SetNextWindowViewport(viewport->ID);

ImGui::PushStyleVar(ImGuiStyleVar_WindowRounding, 0.0f);
ImGui::PushStyleVar(ImGuiStyleVar_WindowBorderSize, 0.0f);
ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(0.0f, 0.0f));

ImGui::Begin("##main", nullptr,
            ImGuiWindowFlags_NoTitleBar | ImGuiWindowFlags_NoCollapse | ImGuiWindowFlags_NoResize |
            ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoBringToFrontOnFocus | ImGuiWindowFlags_NoNavFocus |
            ImGuiWindowFlags_MenuBar | ImGuiWindowFlags_NoBackground);

ImGui::PopStyleVar(3);

m_main_dock_id = ImGui::GetID("main-dock_id");

if (!ImGui::DockBuilderGetNode(m_main_dock_id))
{
    ImGui::DockBuilderRemoveNode(m_main_dock_id);
    ImGui::DockBuilderAddNode(m_main_dock_id, ImGuiDockNodeFlags_PassthruCentralNode | ImGuiDockNodeFlags_DockSpace);
    ImGui::DockBuilderSetNodeSize(m_main_dock_id, viewport->Size);

    ImGuiID rem_dock_id;
    m_bottom_toolbar_dock_id = ImGui::DockBuilderSplitNode(m_main_dock_id, ImGuiDir_Down, 0.15f, nullptr, &rem_dock_id);
    m_left_sidebar_dock_id = ImGui::DockBuilderSplitNode(rem_dock_id, ImGuiDir_Left, 0.2f, nullptr, nullptr);

    ImGui::DockBuilderFinish(m_main_dock_id);
}

ImGui::DockSpace(m_main_dock_id, ImVec2(0, 0), ImGuiDockNodeFlags_PassthruCentralNode);

ImGui::End();

ImGui::PushStyleColor(ImGuiCol_WindowBg, ImVec4(1, 0, 0, 0.1));
ImGui::SetNextWindowDockID(m_left_sidebar_dock_id, ImGuiCond_Once);
ImGui::ShowDemoWindow();
ImGui::PopStyleColor();

What do I expect: Since the main window has no background, I'd expect the docked window's alpha to be kept and be the same as it is when not docked.

[ocornut]

I think WindowBG color is used on dock node indeed.

[loryruta]

I have also tried to force the main window's background colors to transparent:

ImGui::PushStyleColor(ImGuiCol_WindowBg, ImVec4(0,0,0,0));
ImGui::PushStyleColor(ImGuiCol_ChildBg, ImVec4(0,0,0,0));
ImGui::PushStyleColor(ImGuiCol_FrameBg, ImVec4(0,0,0,0));

ImGui::Begin("##main", nullptr, ... ImGuiWindowFlags_NoBackground ...);

// (...)

ImGui::PopStyleColor(3);

But I still have the same issue. How can I keep the docked window background the same?

[ocornut]

Presently i don’t think you can.